When a pest species is introduced into a new environment, immediate concerns are the geographical range it will occupy and the relative impact it will have in different habitats. Relative densities and impact are difficult to predict, but several attempts have been made to predict geographical limits of invading species based on the climatic extremes the species experiences in its native habitats. In theory such predictions should work, since an organism should not be able to tolerate conditions more extreme than those under which it evolved.